The present invention relates generally to the field of removing coke from high temperature hydrocarbon systems.
Thermal management is a significant challenge in advanced aircraft, rocket, and missile engines. Increasing aircraft speed and engine thrust-to-weight ratio results in large, simultaneous increases in heat load and temperature of the air available for cooling. Engine and vehicle cooling must therefore be accomplished by using the fuel as a cooling means. One method of cooling advanced engines is the application of high heat sink fuel cooling technology. Although cryogenic fuels, such as liquid methane and liquid hydrogen, can provide sufficient cooling, they present issues in the areas of cost, logistics, operations, and safety. By contrast, conventional liquid hydrocarbon fuels undergoing endothermic chemical cracking, catalytically and/or thermally, offer the required cooling capacity without the problems associated with cryogenic fuels. The primary products of the endothermic reaction are gaseous fuels with short ignition delay times and rapid burning rates. In addition, waste heat absorbed by the fuel can be returned to the system, enhancing performance and system efficiency.
However, the decomposition of hydrocarbon fuel at elevated temperatures leads to coke deposition within the fuel passages. Coke typically consists of approximately 80% to 95% carbon by weight with the balance comprising sulfur, nitrogen, inorganic materials, ash, and small amounts of oxygen. The coke deposits which form in the heat exchangers, reactors, and on the fuel system component walls degrade heat transfer and fuel flow characteristics and, if left unchecked, can lead to system failure. The extent to which the benefits of high endothermic hydrocarbon fuel cooling technology can be realized is thus directly related to the ability to mitigate against coke formation.